CN115459347A - Method for selecting and cooperatively controlling power supply recovery paths of micro-grid group - Google Patents

Method for selecting and cooperatively controlling power supply recovery paths of micro-grid group Download PDF

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CN115459347A
CN115459347A CN202211241114.6A CN202211241114A CN115459347A CN 115459347 A CN115459347 A CN 115459347A CN 202211241114 A CN202211241114 A CN 202211241114A CN 115459347 A CN115459347 A CN 115459347A
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voltage
microgrid
power supply
power
distributed power
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楼冠男
李山林
顾伟
蒋啸宇
陈畅
赵波
陈哲
李志浩
林达
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Southeast University
Electric Power Research Institute of State Grid Zhejiang Electric Power Co Ltd
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Electric Power Research Institute of State Grid Zhejiang Electric Power Co Ltd
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    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00—Circuit arrangements for ac mains or ac distribution networks
    • H02J3/38—Arrangements for parallely feeding a single network by two or more generators, converters or transformers
    • H02J3/381—Dispersed generators
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00—Circuit arrangements for ac mains or ac distribution networks
    • H02J3/04—Circuit arrangements for ac mains or ac distribution networks for connecting networks of the same frequency but supplied from different sources
    • H02J3/06—Controlling transfer of power between connected networks; Controlling sharing of load between connected networks
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00—Circuit arrangements for ac mains or ac distribution networks
    • H02J3/38—Arrangements for parallely feeding a single network by two or more generators, converters or transformers
    • H02J3/46—Controlling of the sharing of output between the generators, converters, or transformers
    • H02J3/48—Controlling the sharing of the in-phase component
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00—Circuit arrangements for ac mains or ac distribution networks
    • H02J3/38—Arrangements for parallely feeding a single network by two or more generators, converters or transformers
    • H02J3/46—Controlling of the sharing of output between the generators, converters, or transformers
    • H02J3/50—Controlling the sharing of the out-of-phase component

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Abstract

The invention belongs to the technical field of micro-grid group operation control, and discloses a micro-grid group power supply recovery path selection and cooperative control method, which comprises the steps of collecting local voltage and current information through distributed power supplies in each micro-grid group, and obtaining a voltage reference value through droop control; calculating compensation quantity required by reactive power sharing according to capacity and voltage recovery inside each microgrid; then, considering the impact current in the topology switching process, determining the power adjustable range of each micro-grid group, and comparing and selecting the minimum fluctuation-causing power conversion path according to the voltage angle difference at two ends of the power conversion path and the steady-state transmission power of the connecting line; and the smooth grid connection of the original conversion supply region is realized through presynchronization of voltage phase angles of the micro-grid regions at two ends of the connecting line. The method can realize control in the process of topology dynamic change among micro-grid groups, ensure the realization of the equalization of the power supply voltage amplitude, frequency and power of the micro-grid groups, effectively select a proper transfer path, reduce transient fluctuation in the topology switching process and improve the reliability of power supply of the micro-grid groups.

Description

Method for selecting and cooperatively controlling power supply recovery paths of micro-grid group
Technical Field
The invention belongs to the technical field of micro-grid group operation control, and particularly relates to a micro-grid group power supply recovery path selection and cooperative control method.
Background
The micro-grid is an area autonomous grid system formed by various distributed power sources, distributed energy storage, loads and related monitoring and protecting devices. A single micro-grid is difficult to meet flexible load transfer in a fault scene, and the risk resistance is poor.
If a certain line in a microgrid has a sudden fault, the affected source load needs to be converted into power supply through topology conversion to ensure uninterrupted power supply, corresponding research is mainly focused on optimization selection of power supply topology at present, the switch state is represented by a 0-1 two-state value, objective functions of reducing network loss, optimizing power supply cost, improving voltage quality and the like are considered, and optimization problems are solved through various mathematical optimization algorithms, heuristic algorithms and intelligent algorithms, such as genetic algorithms, immune algorithms, particle swarm algorithms, a hybrid method based on various methods and the like, so that a new topological structure is obtained. However, the topology optimization algorithm does not consider the dynamic influence on the microgrid cluster system during the switching action, so that the control problem of each distributed power supply in the microgrid cluster after the instruction is issued needs to be concerned, and how to coordinate the control in the high-density distributed power supply access microgrid cluster to minimize the fluctuation of the switching process and make the transition smooth.
Transient fluctuation when a tie line power reduction switch is disconnected is reduced in advance through increasing of a distributed power source in a microgrid group, but under the scene of sudden faults, affected nodes and source loads need to be cut off and supplied rapidly, power supply reliability is guaranteed as far as possible, operations such as reduction of the power of the tie line in advance are difficult to perform at the moment, meanwhile, an economical supply conversion strategy is difficult to consider in a short time, and the node causing the minimum fluctuation can be selected as far as possible in a supply-capable line to perform load supply conversion.
Disclosure of Invention
Aiming at the defects of the prior art, the invention aims to provide a method for selecting and cooperatively controlling a power supply recovery path of a microgrid group, which solves the problems mentioned in the background technology.
The purpose of the invention can be realized by the following technical scheme:
a method for selecting and cooperatively controlling a power supply recovery path of a micro-grid group comprises the following steps:
a: local voltage and current information is acquired through distributed power supplies in each microgrid group, a voltage reference value is obtained through droop control, and the compensation quantity of reactive power sharing according to capacity and the compensation quantity required by voltage recovery in each microgrid are calculated based on a distributed consistency algorithm;
b: considering impact current in the topology switching process, determining the power adjustable range of each microgrid group, and selecting a switching path causing minimum fluctuation by comparing voltage angle differences at two ends of the switching path and estimated steady-state transmission power of a connecting line;
c: interacting the frequency recovery compensation quantity through a distributed information network based on the selected transfer path to realize the capacity-based equipartition of active power during topology switching;
d: after the fault is recovered, smooth grid connection of the original power supply area is realized through presynchronization of voltage phase angles of microgrid areas at two ends of a connecting line.
Further, in the step a, the reference value E of the voltage is calculated according to the following steps a01 to a04 i ref ：
A01: the control method comprises the following steps:
Figure BDA0003884282230000021
calculating to obtain a distributed power supply output voltage angular frequency reference value omega i And an amplitude reference value E i (ii) a Wherein, subscript i represents the ith distributed power supply; omega i And E i Respectively obtaining an angular frequency reference value and a voltage amplitude reference value of the output voltage of the distributed power supply i; omega * And E * The rated angular frequency and the voltage amplitude of the microgrid system are represented; p i And Q i Respectively obtaining active power and reactive power output by the distributed power supply i through the sampled local voltage and current; m is i And n i Active and reactive droop coefficients, respectively, set to mimic the characteristics of the generator.
A02: considering the poor regulation characteristic of the droop control and the imbalance between the impedances, based on a distributed communication network:
Figure BDA0003884282230000022
calculating compensation quantity delta E required by reactive power sharing according to capacity in microgrid group Qi (ii) a Wherein k is Qp And k Qi The proportional and integral control gains of the Q-U reactive voltage regulation link are represented; a is ij Representing the communication relationship between the partial nodes, a ij >0 indicates that the distributed power sources i and j can exchange information, otherwise, a ij ＝0；n i And n j The reactive droop coefficients of the distributed power source i and the distributed power source j are respectively, and the values of the reactive droop coefficients are inversely proportional to the capacity; q i And Q j Respectively the reactive outputs of the distributed power supply i and the distributed power supply j; n is a radical of i Is shown andthe ith distributed power supply connected set;
a03: based on a dynamic consistency observer:
Figure BDA0003884282230000031
calculating the compensation amount delta E required for recovering the global average voltage in the microgrid to a standard value Vi (ii) a Wherein the content of the first and second substances,
Figure BDA0003884282230000032
and
Figure BDA0003884282230000033
the global average voltage estimated at the distributed power source i and the distributed power source j respectively; e i Is the voltage amplitude output by the distributed power source i; eta E Is the voltage recovery gain factor; k is a radical of Ei Is a voltage integral control gain term; e ref Is a reference voltage set by the microgrid system;
a04: equally dividing the reactive power in each microgrid by the compensation quantity delta E required by capacity Qi And the compensation amount Δ E required to restore the global average voltage to the standard value Vi Adding the voltage values and the droop control link to obtain a reference value of the output voltage of the distributed power supply i
Figure BDA0003884282230000034
As follows.
Figure BDA0003884282230000035
Further, in the step B, a handover path is selected according to the following steps B01 to B05:
b01: solving the zero state response of the equivalent circuit when the switch is closed to obtain the impact current on the connecting line when the switch is closed as follows:
Figure BDA0003884282230000036
wherein the content of the first and second substances,
Figure BDA0003884282230000037
the amplitude of the periodic component of the impulse current is shown, wherein Em is the amplitude of the equivalent voltage on two sides of the switch, and R, L is the resistance and the inductance of the transmission line where the switch is located respectively; ω is the angular frequency of the system; alpha is the phase angle of the equivalent voltage at two sides of the switch;
Figure BDA0003884282230000038
is the switch closure and the impedance angle of the distribution network; t is a Is the decay time constant of the rush current on the tie line, and T a ＝L/R；
B02: defining the adjustable range of the power supply required by the fault area and the power of the microgrid which can be supplied to the fault area:
Figure BDA0003884282230000039
if the power adjustable range of the micro-grid is larger than the requirement, the micro-grid can be supplied; wherein, Δ P max And Δ P min Respectively upper and lower limits of the cluster's active adjustable range, Δ Q max And Δ Q min Respectively the upper and lower limits, P, of the reactive adjustable range of the cluster i max 、P i min 、Q i max 、Q i min Respectively the maximum value and the minimum value, P, of the active power output and the reactive power output of the distributed power supply i i And Q i The active and reactive output of the distributed power supply i at the current moment is M, and M is a set of controllable distributed power supplies in the corresponding microgrid;
b03: phase angles of phase-locked loops formed by a second-order generalized integrator DSOGI are respectively extracted from voltages of the micro-grids on two sides of a tie line, and then phase angle differences delta theta at two ends of a transferable path between micro-grid groups are obtained; simultaneously, extracting voltage fundamental wave information at two ends of a transferable path respectively through fast Fourier transform, thereby obtaining a voltage difference delta E at two ends of the transferable path between the microgrid groups;
b04: the steady state current size after the tie line switch closes also can exert an influence to the transient state fluctuation when the switch closes, but the current size that will appear on the tie line is difficult to know, consequently replaces the power size that will pass through the tie line transmission through predicting the power variation volume after each distributed power source adds different little electric wire netting in this fault area:
Figure BDA0003884282230000041
wherein, Δ P i And Δ Q i Adding different active and reactive variable quantities which can be supplied to the microgrid for each distributed power supply in the fault area; y and X are respectively a fault area Y and a set of distributed power supplies to be supplied to the microgrid cluster X, c i Is a proportionality coefficient, P, inversely proportional to the i capacity of the distributed power supply i And Q i For distributing real-time active and reactive power of the power supply i, n Y And n X The number of distributed power supplies of a fault area Y and a to-be-supplied area X are respectively;
b05: transient fluctuation results caused by path selection are compared by a micro-grid group system formed by three micro-grids according to phase angle differences, voltage differences and the magnitude of steady-state transmission current of tie lines respectively, so that the influence of the phase angle differences on transient fluctuation when a switch is closed can be considered to be the largest, the influence of the magnitude of the steady-state transmission current of the tie lines is the next to the magnitude of the steady-state transmission current of the tie lines, and the influence of the difference of voltage amplitudes on two sides of the switch is the smallest; accordingly, a switch-over path is selected after a sudden failure occurs in the microgrid group.
Further, in the step B02, Q i max And Q i min Value and current active power output P of distributed power supply i Regarding, limited by the power factor, the expression is as follows:
Q i max ＝-Q i min ＝|P i tanθ i equation (7)
Wherein theta is i Representing the power factor angle.
Further, in the step B05, the step of selecting a transfer path after the sudden failure in the microgrid group is as follows:
firstly, comparing whether the power adjustable range of each transferable region meets the power requirement in the fault region, namely delta P min <P need <ΔP max And is Δ Q min <Q need <ΔQ max ；
Secondly, comparing phase angle differences at two ends of different links among sub-areas meeting power requirements, and selecting a link min (delta theta) with the minimum phase angle difference;
then, if the phase angle difference of the two ends of the connecting line is the same, comparing the variation of the distributed power supply output in the fault area when the connecting line is connected to different sub-areas, and selecting the connecting line min (delta P) with the least variation i +ΔQ i )；
And finally, if the links with similar variation exist, selecting the link with the smallest voltage amplitude difference to transfer the link for min (delta E).
Further, in the step C, the active power sharing during topology switching is realized according to the following steps C01 to C02:
c01: considering the poor regulation characteristic of droop control, each distributed power supply in the microgrid needs to compensate the output frequency for recovering the system frequency to a standard value:
Δω i ＝k ωp (ω ref -ω i )+k ωi ∫(ω ref -ω i ) Formula (9)
Wherein, Δ ω i Restoring compensation quantity for angular frequency formed by each distributed power supply in the microgrid through local information; k is a radical of ωp And k ωi The proportional and integral control gain of the P-f active frequency regulation link is represented; omega i Is the angular frequency of the distributed power source i output; omega ref Is the reference angular frequency of the microgrid system;
c02: in order to ensure that the active power can still be equally divided in the topology switching process, a distributed consistency strategy is introduced to ensure that the active output droop curves of all distributed power supplies tend to be synchronous, and meanwhile, a droop control link is added, so that a reference value omega refi of the output angular frequency of the distributed power supply i is obtained as follows:
Figure BDA0003884282230000051
further, in the step D, smooth grid connection of the original transfer supply region is realized according to the following step D01:
Figure BDA0003884282230000052
after the fault is recovered, smooth grid connection of the original power supply conversion area is realized through presynchronization of voltage phase angles of microgrid areas at two ends of a connecting line; wherein, Δ ω 'i and Δ E' i are added pre-synchronization compensation terms to achieve synchronization of phase angles and voltage amplitudes at two sides before switching; delta XY Representing the switching state, delta, connecting the transshipment area X and the microgrid area Y XY =1 indicating that the switch is about to be closed, δ XY =0 indicates that the switch remains open; k is a radical of ui,XY And k Ei,XY Respectively corresponding integral controller gains; u. of qX And u qY Representing phase angle difference by q-axis component difference generated by the same voltage under different phase angles on two sides of the switch for the difference of q-axis components after the voltage on two sides of the switch is subjected to Park change; e X And E Y The difference in magnitude of the voltage across the switch is then indicated.
The invention has the beneficial effects that:
compared with the optimized switch switching plan, the micro-grid group power supply recovery path selection and cooperative control method provided by the invention considers transient fluctuations such as impact current in switch switching, and provides a control method capable of quickly selecting a switching path among micro-grid groups; in the invention, considering that the distributed frequency recovery and active power capacity-based sharing links can cause sharing failure due to dynamic adjustment during topology change, a distributed consistency strategy is introduced to ensure that active power output droop curves of all distributed power supplies tend to be synchronous, and capacity-based sharing of active power is realized during topology switching. The cooperative control performance of the micro-grid group is improved, and the power supply reliability is improved.
Drawings
In order to more clearly illustrate the embodiments or technical solutions in the prior art of the present invention, the drawings used in the description of the embodiments or prior art will be briefly described below, and it is obvious for those skilled in the art that other drawings can be obtained based on these drawings without creative efforts.
FIG. 1 is a flow chart of a method for selecting switching between micro-grid inter-group switches in a fault scenario designed by the present invention;
FIG. 2 is a flow chart of the fault path selection designed to account for switching inrush current;
FIG. 3 is a diagram of a microgrid cluster simulation system employed in an embodiment of the present invention;
fig. 4 is a phase angle difference diagram of a branch when a microgrid group selects a supply path according to a phase angle difference;
fig. 5 is a node frequency fluctuation graph when the microgrid group selects a supply path according to a phase angle difference;
fig. 6 is an active power waveform diagram of each distributed power source in the microgrid group when a supply path is selected according to a phase angle difference;
fig. 7 is a reactive power waveform diagram of each distributed power source in the microgrid group when a switching path is selected according to a phase angle difference;
FIG. 8 is a graph of voltage per unit values of nodes before and after topology change when a microgrid group selects a supply path according to phase angle difference
Fig. 9 is a graph of branch voltage differences when the microgrid group selects a transfer path according to the voltage difference;
fig. 10 is a node frequency fluctuation diagram when the microgrid group selects a transfer path according to a voltage difference;
fig. 11 is a schematic diagram of the tie line power when the piconet group selects the handover path according to the estimated tie line power;
fig. 12 is a graph of node frequency fluctuation for the piconet group when selecting a switch path according to the estimated tie line power.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
As shown in fig. 1-2, the present invention designs a method for selecting and cooperatively controlling a power supply restoration path of a microgrid group, which in practical application specifically includes the following steps:
step A: collecting local voltage and current information through distributed power supplies in each microgrid group, obtaining a voltage reference value through droop control, calculating compensation quantity required by reactive power capacity sharing and voltage recovery in each microgrid based on a distributed consistency algorithm, and entering the step B;
and B: calculating impact current in the topology switching process, determining the power adjustable range of each microgrid group, selecting a switching path causing minimum fluctuation by comparing the voltage angle difference of two ends of the switching path and the estimated steady-state transmission power of the connecting line, and then entering the step C;
and C: interacting the frequency recovery compensation quantity through a distributed information network based on the selected transfer path to realize that the active power is uniformly divided according to the capacity during topology switching, and then entering the step D;
step D: after the fault is recovered, smooth grid connection of the original power supply area is realized through presynchronization of voltage phase angles of microgrid areas at two ends of a connecting line.
In the step a, the reference value E of the voltage is calculated according to the following steps a01 to a04 i ref ：
Step A01: the control method comprises the following steps:
Figure BDA0003884282230000071
calculating to obtain a distributed power supply output voltage angular frequency reference value omega i And an amplitude reference value E i (ii) a Wherein, subscript i represents the ith distributed power supply; omega i And E i Are respectively distributed power suppliesi outputting an angular frequency reference value and a voltage amplitude reference value of the voltage; omega * And E * The rated angular frequency and the voltage amplitude of the microgrid system are represented; p is i And Q i Respectively obtaining active power and reactive power output by the distributed power supply i through the sampled local voltage and current; m is i And n i Active and reactive droop coefficients, respectively, set to mimic the characteristics of the generator.
Step A02: considering the poor regulation characteristic of the droop control and the imbalance between the impedances, based on a distributed communication network:
Figure BDA0003884282230000072
calculating compensation quantity delta E required by reactive power sharing according to capacity in microgrid group Qi (ii) a Wherein k is Qp And k Qi The proportional and integral control gains of a Q-U reactive voltage regulation link are expressed, and the reactive power output by each distributed power supply can be equally divided according to the capacity through the compensation quantity generated by the link; a is a ij Representing the communication relationship between the partial nodes, a ij >0 indicates that the distributed power sources i and j can exchange information, otherwise, a ij ＝0；n i And n j The reactive droop coefficients of the distributed power source i and the distributed power source j are respectively, and the values of the reactive droop coefficients are inversely proportional to the capacity; q i And Q j Respectively the reactive outputs of the distributed power supply i and the distributed power supply j; n is a radical of i Representing the set of connections to the ith station distributed power supply.
Step A03: based on a dynamic consistency observer:
Figure BDA0003884282230000081
calculating the compensation amount delta E required for recovering the global average voltage in the microgrid to a standard value Vi (ii) a Wherein the content of the first and second substances,
Figure BDA0003884282230000082
and
Figure BDA0003884282230000083
the global average voltages estimated at distributed power source i and distributed power source j, respectively; e i Is the voltage amplitude output by the distributed power source i; eta E Is the voltage recovery gain factor; k is a radical of formula Ei Is a voltage integral control gain term; e ref Is a reference voltage set by the microgrid system.
Step A04: equally dividing the reactive power in each microgrid by the compensation quantity delta E required by capacity Qi And the compensation amount Δ E required to restore the global average voltage to the standard value Vi Adding, adding droop control link, and outputting reference value of voltage of distributed power supply i
Figure BDA0003884282230000084
Can be expressed as:
Figure BDA0003884282230000085
in the step B, the switching path is selected according to the following steps B01 to B05:
step B01: solving the zero state response of the equivalent circuit when the switch is closed to obtain the impact current on the connecting line when the switch is closed as follows:
Figure BDA0003884282230000086
wherein, the first and the second end of the pipe are connected with each other,
Figure BDA0003884282230000087
the amplitude of the periodic component of the impulse current is shown, wherein Em is the amplitude of the equivalent voltage on two sides of the switch, and R, L is the resistance and the inductance of the transmission line where the switch is located respectively; ω is the angular frequency of the system; alpha is the phase angle of the equivalent voltage at two sides of the switch;
Figure BDA0003884282230000088
is the switch closure and the impedance angle of the distribution network; t is a For surge currents on the interconnection lineDecay time constant, and T a And (= L/R). It can be seen that the large impact on the inrush current includes the phase angle difference across the switch closure, the voltage amplitude difference, and the steady state current value.
Step B02: defining the adjustable range of the power supply required by the fault area and the power of the microgrid which can be supplied to the fault area:
Figure BDA0003884282230000091
if the micro-grid power adjustable range is larger than the required range, the micro-grid power can be supplied; wherein, Δ P max And Δ P min Respectively upper and lower limits of the cluster's active adjustable range, Δ Q max And Δ Q min Respectively the upper and lower limits, P, of the reactive adjustable range of the cluster i max 、P i min 、Q i max 、Q i min Respectively the maximum value and the minimum value, P, of the active power output and the reactive power output of the distributed power supply i i And Q i And M is the set of the controllable distributed power supplies in the corresponding micro-grid. At the same time, Q i max And Q i min Value and current active power output P of distributed power supply i In relation to, limited by the power factor, the expression is as follows, where θ i Representing the power factor angle:
Q i max ＝-Q i min ＝|P i tanθ i equation (7)
Step B03: phase angles of phase-locked loops formed by a second-order generalized integrator DSOGI are respectively extracted from voltages of micro-grids on two sides of a tie line, then phase angle differences delta theta between two ends of a transferable path among micro-grid groups are obtained, and influences of harmonic waves, unbalanced components and the like on phase angle extraction can be avoided; and simultaneously, extracting voltage fundamental wave information at two ends of the transferable path respectively through fast Fourier transform, thereby obtaining the voltage difference delta E at two ends of the transferable path between the micro-grid groups.
Step B04: the steady state current size after the tie line switch closes also can exert an influence to the transient state fluctuation when the switch closes, but the current size that will appear on the tie line is difficult to know, consequently replaces the power size that will pass through the tie line transmission through predicting the power variation volume after each distributed power source adds different little electric wire netting in this fault area:
Figure BDA0003884282230000092
wherein, Δ P i And Δ Q i Adding different active and reactive variable quantities which can be supplied to the microgrid for each distributed power supply in the fault area; y and X are respectively a fault area Y and a set of distributed power supplies to be supplied to the microgrid cluster X, c i Is a proportionality coefficient, P, inversely proportional to the i capacity of the distributed power supply i And Q i For distributing real-time active and reactive power of the power supply i, n Y And n X The number of power supplies distributed for the fault zone Y and the zone X to be switched over, respectively.
Step B05: transient fluctuation results caused by path selection are compared by a micro-grid group system formed by three micro-grids according to phase angle differences, voltage differences and the magnitude of steady-state transmission current of the tie lines, so that the influence of the phase angle differences on transient fluctuation when the switch is closed is the largest, the influence of the magnitude of the steady-state transmission current of the tie lines is the next to the magnitude of the steady-state transmission current of the tie lines is the smallest, and the influence of the voltage amplitude difference on the two sides of the switch is the smallest. Therefore, the switching selection steps after the sudden failure in the microgrid group are as follows:
firstly, comparing whether the power adjustable range of each transferable region meets the power requirement in the fault region, namely delta P min <P need <ΔP max And is Δ Q min <Q need <ΔQ max ；
Secondly, comparing phase angle differences at two ends of different links among sub-areas meeting power requirements, and selecting a link min (delta theta) with the minimum phase angle difference;
then, if the phase angle difference of the two ends of the connecting line is the same, comparing the variation of the distributed power supply output in the fault area when the connecting line is connected to different sub-areas, and selecting the connecting line min (delta P) with the least variation i +ΔQ i )；
Finally, if there are links with similar variation, the link with the smallest voltage amplitude difference is selected for min (Δ E) forwarding.
In the step C, the active power sharing during topology switching is realized according to the following steps C01 to C02:
step C01: considering the poor regulation characteristic of droop control, each distributed power supply in the microgrid needs to compensate the output frequency for recovering the system frequency to a standard value:
Δω i ＝k ωp (ω ref -ω i )+k ωi ∫(ω ref -ω i ) Formula (9)
Wherein, Δ ω i Restoring compensation quantity for angular frequency formed by each distributed power supply in the microgrid through local information; k is a radical of ωp And k ωi The proportional and integral control gains of the P-f active frequency adjusting link are represented, and the system frequency can be restored to a standard value through the compensation quantity generated by the link; omega i Is the angular frequency of the distributed power source i output; omega ref Is the reference angular frequency of the microgrid system setting.
Step C02: in order to ensure that the active power can still be equally divided in the topology switching process, a distributed consistency strategy is introduced to ensure that the active output droop curves of all distributed power supplies tend to be synchronous, and meanwhile, a droop control link is added, so that a reference value omega refi of the output angular frequency of the distributed power supply i is obtained as follows:
Figure BDA0003884282230000101
wherein k is Pi The integral control gain which ensures that the active output droop curve of each distributed power supply tends to a synchronous link is represented; a is ij Representing the communication relation between the partial nodes; Δ ω j The compensation amount is recovered for the local angular frequency of the distributed power source j in the same distributed communication network as the distributed power source i, and the calculation is shown in the formula (9).
In the step D, smooth grid connection of the original transfer supply area is realized according to the following step D01:
Figure BDA0003884282230000111
after the fault is recovered, smooth grid connection of the original power supply conversion area is realized through presynchronization of voltage phase angles of microgrid areas at two ends of a connecting line; wherein, Δ ω 'i and Δ E' i are added pre-synchronization compensation terms to achieve synchronization of phase angles and voltage amplitudes at two sides before switching; delta XY Representing the switching state, delta, connecting the transshipment area X and the microgrid area Y XY =1 indicating that the switch is about to be closed, δ XY =0 indicates that the switch remains open; k is a radical of ui,XY And k Ei,XY Respectively, corresponding integral controller gains. u. of qX And u qY Representing phase angle difference by q-axis component difference generated by the same voltage under different phase angles on two sides of the switch for the difference of q-axis components after the voltage on two sides of the switch is subjected to Park change; e X And E Y The difference in magnitude of the voltage across the switch is then indicated.
The designed technical scheme is applied to the practice, the simulation system is shown in fig. 3, three micro-grids form a micro-grid group, eight distributed power supplies exist, rated active and reactive capacities of the eight distributed power supplies are equal, and meanwhile, in order to enable the switching path selection under the fault scene to be more contrastive, a plurality of connecting lines are added among areas. According to the method for switching and selecting the switches among the microgrid groups in the fault scene, a simulation microgrid group model is built based on an MATLAB/Simulink platform, and the control effect of the method is verified.
Fig. 4 to 12 show simulation results of the microgrid group control in the present embodiment. At the beginning of operation, each distributed power supply operates in a droop control mode. The most frequently occurring and most influential faults in the power system are single-phase ground faults, so this section takes an a-phase short fault as an example to verify the validity of the proposed path selection strategy. The method comprises the following steps that a single-phase earth fault occurs between the branches 2-5 at t =1.95s, the detection and action time of the relay protection device is about 0.05s, the branches 2-5 are disconnected when t =2s is set, and at the moment, three transfer paths exist in source load of a node 5: branch 5-3, branch 5-6 and branch 5-7, select to close the corresponding tie switch based on the switch-over path policy described in the previous section. Fig. 4 shows a branch phase angle difference when the supply path is selected according to the phase angle difference, and the abscissa represents time in units: second, the ordinate represents the phase angle difference, in units: and (4) radian. As can be seen from fig. 4, the phase angle difference between the node 5 and the node 7 is the smallest before the 1.95s fault occurs, but due to the occurrence of the fault, the distributed power supply in the microgrid 1 generates a large impact in a short time to change the real-time phase angle difference, and when the phase angle difference between the node 5 and the node 6 is the smallest at 2s turn-on, the branch 5-6 is selected for the turn-on of the source load. Fig. 5 is a node frequency fluctuation diagram when a supply path is selected by a phase angle difference, and the abscissa represents time in units of: second, ordinate represents frequency, unit: hertz. As shown in FIG. 5, the fluctuation caused by the nodes at both ends of the transfer path is very small, and is 0.032 Hz. Fig. 6 is an active power waveform when the transfer path is selected by phase angle difference, and the abscissa represents time in units of: second, the ordinate represents the active power, in units: and (4) tile. Fig. 7 is a reactive power waveform when a transfer path is selected by a phase angle difference, and the abscissa represents time in units of: second, the ordinate represents reactive power, in units: it is used for treating chronic hepatitis B. As can be seen from fig. 6 and 7, when a sudden ground fault occurs at t =1.95s, the distributed power sources in the first microgrid generate large power fluctuations, and after the supply starts at t =2s, the distributed power sources can quickly and smoothly implement corresponding active and reactive power distribution according to new region division. Fig. 8 shows voltage per unit values of each node before and after topology change when a supply path is selected according to a phase angle difference, where an abscissa represents time and a unit: second, the ordinate represents the voltage per unit value. As shown in fig. 8, the voltage per unit value of each node is between 0.95 and 1.05 before and after the topology change, and both nodes operate within the range allowed by the voltage quality. Fig. 9 is a branch voltage difference when the transfer path is selected according to the voltage difference, and the abscissa represents time in units: second, the ordinate represents the voltage difference per unit. As can be seen from fig. 9, the voltage difference between node 5 and node 7 is the smallest at 2s turn-up, so that branch 5-7 is selected for source charge turn-up. Fig. 10 is a node frequency fluctuation diagram when a transfer path is selected according to a voltage difference, and the abscissa represents time in units of: second, ordinate represents frequency, unit: hertz. As shown in fig. 10, the fluctuation caused by the nodes at the two ends of the transfer path is very large, and is 0.115 hz. Fig. 11 is a graph of tie line power when a switch path is selected according to the estimated tie line power, with the abscissa representing time in units: second, ordinate represents power, unit: and (4) tile. As can be seen from fig. 11, the estimated tie line power on branch 5-6 is the smallest at 2s trans-supply, so branch 5-6 is selected for source load trans-supply. Fig. 12 is a graph of node frequency fluctuation when selecting a transfer path according to the estimated tie line power, where the abscissa represents time in units: second, ordinate represents frequency, unit: hertz. As shown in fig. 12, the fluctuation caused by the nodes at the two ends of the feeding path is slightly larger than the fluctuation caused by feeding according to the phase angle difference, and is 0.045 hz. Through the supply comparison of the three influencing factors, the fluctuation selected according to the phase angle difference is minimum, the fluctuation is reduced by 72.2% compared with the fluctuation selected according to the voltage difference, and the fluctuation is reduced by 28.9% compared with the fluctuation selected according to the estimated steady-state power, so that the influence of the phase angle difference on the transient fluctuation when the switch is closed is maximum, the influence of the steady-state transmission current of the tie line is the second order, and the influence of the voltage amplitude difference on the two sides of the switch is minimum.
Compared with the switch switching planning of an optimization layer, the method for selecting and cooperatively controlling the power supply recovery paths of the micro-grid groups considers transient fluctuations such as impact current in switch switching, and provides a control method capable of quickly selecting the switching paths among the micro-grid groups; in the invention, considering that the distributed frequency recovery and active power capacity-based sharing links can cause sharing failure due to dynamic adjustment during topology change, a distributed consistency strategy is introduced to ensure that active power output droop curves of all distributed power supplies tend to be synchronous, and capacity-based sharing of active power is realized during topology switching. The cooperative control performance of the micro-grid group is improved, and the power supply reliability is improved.
In the description herein, references to the description of "one embodiment," "an example," "a specific example" or the like are intended to mean that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the invention. In this specification, the schematic representations of the terms used above do not necessarily refer to the same embodiment or example. Furthermore, the particular features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.
The foregoing shows and describes the general principles, essential features, and advantages of the invention. It will be understood by those skilled in the art that the present invention is not limited to the embodiments described above, which are described in the specification and illustrated only to illustrate the principle of the present invention, but that various changes and modifications may be made therein without departing from the spirit and scope of the present invention, which fall within the scope of the invention as claimed.

Claims (7)

1. A method for selecting and cooperatively controlling a power supply recovery path of a micro-grid group is characterized by comprising the following steps:
a: local voltage and current information is acquired through distributed power supplies in each microgrid group, a voltage reference value is obtained through droop control, and the compensation quantity of reactive power sharing according to capacity and the compensation quantity required by voltage recovery in each microgrid are calculated based on a distributed consistency algorithm;
b: considering impact current in the topology switching process, determining the power adjustable range of each micro-grid group, and selecting a power conversion path causing minimum fluctuation by comparing voltage angle differences at two ends of the power conversion path and estimated steady-state transmission power of a connecting line;
c: interacting the frequency recovery compensation quantity through a distributed information network based on the selected transfer path to realize the capacity-based equipartition of active power during topology switching;
d: after the fault is recovered, smooth grid connection of the original power supply area is realized through presynchronization of voltage phase angles of microgrid areas at two ends of a connecting line.
2. The method for selecting and cooperatively controlling the power restoration paths of the microgrid group according to claim 1, characterized in that; in the step A, the reference value E of the voltage is calculated according to the following steps A01 to A04 i ref ：
A01: the control method comprises the following steps:
Figure FDA0003884282220000011
calculating to obtain a distributed power supply output voltage angular frequency reference value omega i And amplitude reference value E i (ii) a Wherein, subscript i represents the ith distributed power supply; omega i And E i Respectively obtaining an angular frequency reference value and a voltage amplitude reference value of the output voltage of the distributed power supply i; omega * And E * The rated angular frequency and the voltage amplitude of the microgrid system are represented; p i And Q i Respectively obtaining active power and reactive power output by the distributed power supply i through the sampled local voltage and current; m is i And n i Active and reactive droop coefficients, respectively, set to mimic the characteristics of the generator.
A02: considering the poor regulation characteristic of the droop control and the imbalance between the impedances, based on a distributed communication network:
Figure FDA0003884282220000012
calculating compensation quantity delta E required by reactive power sharing according to capacity in microgrid group Qi (ii) a Wherein k is Qp And k Qi The proportional and integral control gains of the Q-U reactive voltage regulation link are represented; a is ij Representing the communication relationship between the partial nodes, a ij >0 represents that the distributed power supplies i and j can interact with information, otherwise, a ij ＝0；n i And n j The reactive droop coefficients of the distributed power source i and the distributed power source j are respectively, and the values of the reactive droop coefficients are inversely proportional to the capacity; q i And Q j Respectively the reactive outputs of the distributed power supply i and the distributed power supply j; n is a radical of i Representing a set of connections to the ith distributed power supply;
a03: based on a dynamic consistency observer:
Figure FDA0003884282220000021
calculating the compensation amount delta E required for recovering the global average voltage in the microgrid to a standard value Vi (ii) a Wherein, the first and the second end of the pipe are connected with each other,
Figure FDA0003884282220000022
and
Figure FDA0003884282220000023
the global average voltages estimated at distributed power source i and distributed power source j, respectively; e i Is the voltage amplitude output by the distributed power source i; eta E Is the voltage recovery gain factor; k is a radical of formula Ei Is a voltage integral control gain term; e ref Is a reference voltage set by the microgrid system;
a04: equally dividing the reactive power in each microgrid by the compensation quantity delta E required by capacity Qi And a compensation amount Δ E required to restore the global average voltage to a standard value Vi Adding the obtained values, and adding a droop control link to obtain a reference value of the output voltage of the distributed power supply i
Figure FDA0003884282220000024
As follows.
Figure FDA0003884282220000025
3. The method for selecting and cooperatively controlling the power restoration paths of the microgrid group according to claim 1, characterized in that; in the step B, a transfer path is selected according to the following steps B01 to B05:
b01: solving the zero state response of the equivalent circuit when the switch is closed to obtain the impact current on the connecting line when the switch is closed as follows:
Figure FDA0003884282220000026
wherein the content of the first and second substances,
Figure FDA0003884282220000027
the amplitude of the periodic component of the impulse current is shown, wherein Em is the amplitude of the equivalent voltage on two sides of the switch, and R, L is the resistance and the inductance of the transmission line where the switch is located respectively; ω is the angular frequency of the system; alpha is the phase angle of the equivalent voltage at two sides of the switch;
Figure FDA0003884282220000028
closing the switch and the impedance angle of the distribution network; t is a Is the decay time constant of the rush current on the tie line, and T a ＝L/R；
B02: defining the adjustable range of the power supply required by the fault area and the power of the microgrid which can be supplied to the fault area:
Figure FDA0003884282220000031
if the power adjustable range of the micro-grid is larger than the requirement, the micro-grid can be supplied; wherein, Δ P max And Δ P min Respectively, upper and lower limits, Δ Q, of the cluster's active adjustable range max And Δ Q min Respectively the upper and lower limits, P, of the reactive adjustable range of the cluster i max 、P i min 、Q i max 、Q i min Respectively the maximum value and the minimum value, P, of the active power output and the reactive power output of the distributed power supply i i And Q i The active and reactive output of the distributed power supply i at the current moment is M, and M is a set of controllable distributed power supplies in the corresponding microgrid;
b03: phase angles of phase-locked loops formed by a second-order generalized integrator DSOGI are respectively extracted from voltages of the micro-grids on two sides of a tie line, and then phase angle differences delta theta at two ends of a transferable path between micro-grid groups are obtained; simultaneously, extracting voltage fundamental wave information at two ends of a transferable path respectively through fast Fourier transform, thereby obtaining a voltage difference delta E at two ends of the transferable path between the microgrid groups;
b04: the steady state current size after the tie line switch closes also can exert an influence to the transient state fluctuation when the switch closes, but the current size that will appear on the tie line is difficult to know, consequently replaces the power size that will pass through the tie line transmission through predicting the power variation volume after each distributed power source adds different little electric wire netting in this fault area:
Figure FDA0003884282220000032
wherein, Δ P i And Δ Q i Adding different active and reactive variable quantities which can be supplied to the microgrid for each distributed power supply in the fault area; y and X are respectively a fault area Y and a set of distributed power supplies to be converted into a microgrid cluster X, c i Is a proportionality coefficient, P, inversely proportional to the i capacity of the distributed power supply i And Q i For distributing real-time active and reactive power of the power supply i, n Y And n X The number of distributed power supplies of a fault area Y and a to-be-supplied area X are respectively;
b05: transient fluctuation results caused by path selection are compared by a micro-grid group system formed by three micro-grids according to phase angle differences, voltage differences and the magnitude of steady-state transmission current of tie lines respectively, so that the influence of the phase angle differences on transient fluctuation when a switch is closed can be considered to be the largest, the influence of the magnitude of the steady-state transmission current of the tie lines is the next to the magnitude of the steady-state transmission current of the tie lines, and the influence of the difference of voltage amplitudes on two sides of the switch is the smallest; accordingly, a switch-over path is selected after a sudden failure occurs in the microgrid group.
4. The method for selecting and cooperatively controlling the power restoration paths of the microgrid group according to claim 3, characterized in that; in said step B02, Q i max And Q i min Value and current active power output P of distributed power supply i Regarding, limited by the power factor, the expression is as follows:
Figure FDA0003884282220000041
wherein theta is i Representing the power factor angle.
5. The method for selecting and cooperatively controlling the power restoration paths of the microgrid group according to claim 3, characterized in that; in step B05, the steps of selecting a transfer path after the sudden failure in the microgrid group are as follows:
firstly, comparing whether the power adjustable range of each transferable region meets the power requirement in the fault region, namely delta P min <P need <ΔP max And is Δ Q min <Q need <ΔQ max ；
Secondly, comparing phase angle differences at two ends of different links among sub-areas meeting power requirements, and selecting a link min (delta theta) with the minimum phase angle difference;
then, if the phase angle difference of the two ends of the connecting line is the same, comparing the variation of the distributed power supply output in the fault area when the connecting line is connected to different sub-areas, and selecting the connecting line min (delta P) with the least variation i +ΔQ i )；
Finally, if there are links with similar variation, the link with the smallest voltage amplitude difference is selected for min (Δ E) forwarding.
6. The method for selecting and cooperatively controlling the power restoration paths of the microgrid group according to claim 1, characterized in that; in the step C, the active power equipartition during topology switching is realized according to the following steps C01 to C02:
c01: considering the poor regulation characteristic of droop control, each distributed power supply in the microgrid needs to compensate the output frequency for recovering the system frequency to a standard value:
Δω i ＝k ωp (ω ref -ω i )+k ωi ∫(ω ref -ω i ) Formula (9)
Wherein, Δ ω i Corners formed by local information for distributed power sources within a microgridA frequency recovery compensation amount; k is a radical of ωp And k ωi The proportional and integral control gain of the P-f active frequency regulation link is represented; omega i Is the angular frequency of the distributed power source i output; omega ref Is the reference angular frequency of the microgrid system;
c02: in order to ensure that the active power can still be equally divided in the topology switching process, a distributed consistency strategy is introduced to ensure that the active output droop curves of all distributed power supplies tend to be synchronous, and meanwhile, a droop control link is added, so that a reference value omega refi of the output angular frequency of the distributed power supply i is obtained as follows:
Figure FDA0003884282220000051
7. the method for selecting and cooperatively controlling the power restoration paths of the microgrid group according to claim 1, characterized in that; in the step D, smooth grid connection of the original transfer supply area is realized according to the following step D01:
Figure FDA0003884282220000052
after the fault is recovered, smooth grid connection of the original power supply conversion area is realized through presynchronization of voltage phase angles of microgrid areas at two ends of a connecting line; wherein, Δ ω 'i and Δ E' i are added pre-synchronization compensation terms to achieve synchronization of phase angles and voltage amplitudes at two sides before switching; delta XY Representing the switching state, delta, connecting the transshipment area X and the microgrid area Y XY =1 indicating that the switch is about to be closed, δ XY =0 means that the switch remains open; k is a radical of ui,XY And k Ei,XY Respectively corresponding integral controller gains; u. u qX And u qY Representing phase angle difference by q-axis component difference generated by the same voltage under different phase angles on two sides of the switch for the difference of q-axis components after the voltage on two sides of the switch is subjected to Park change; e X And E Y The difference in magnitude of the voltage across the switch is then indicated.
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